Laser printers are one of the most ubiquitous and useful equipment pieces in business and residential computing/document-handling environments. Their print engines employ a replaceable cartridge containing photoconductive drum that transfers black and white (or color) toner particles from a tank containing a reserve of such toner to a print medium, such as paper. The toner is electrostatically charged so that it is drawn from the tank onto a magnetized developer roller or other means that turns in conjunction with the photoconductive drum. The layer of toner deposited on the drum is then transferred to the charged regions of the drum. These charged regions conform to the image-to-be-printed, and are formed by a moving light beam (typically a solid-state laser) under the control of a print driver. The drum transfers the toner in the regions to the medium (e.g. paper) as moves against the rotating drum. After applying the toner to the medium, the drum passes through a wiper that removes any excess toner and a corona unit that de-charges the drum for re-exposure by the laser.
Many commercially available cartridges, such as the E360 series by Lexmark International, Inc. of Lexington, Ky., are provided as two-piece cartridge systems. That is, the tank and developer assembly is removably cradled within a photoconductive drum assembly. A gear train interconnects the drum to the tank assembly. In this manner, the less expensive tank components can be recycled when toner is exhausted, while the more-expensive and longer-lived drum assembly is retained. This increases the efficiency of the toner cartridge life-cycle by attending to the replacement of an exhausted toner supply, while avoiding the need to deal with the photoconductive drum until its service life is actually near an end.
Toner tanks are filled to a predetermined level by the original equipment manufacturer (OEM). In general, that level is less than the total volume of the tank. Many manufactures, such as Clarity Imaging Technologies, Inc. of Springfield, Mass., provide extended life versions of OEM cartridges that are more economical for users, and also more environmentally friendly, due to their longer life and less-frequent change-out schedule. A variety of proprietary techniques are employed to provide an extended life performance. One aspect of this technique is adding more toner to the tank than that provided by the OEM. For an extended-life cartridge to function properly with an increased toner level, modification of a variety of cartridge functions and parameters, such as the agitator timing, is typically required.
A particular consequence of an increased toner load in the cartridge tank is that the internal seals, which normally act to prevent loss of toner to the environment may be overwhelmed. One such seal is formed between the developer roller and its confronting doctor blade. By way of example, when performing a so-called “drop test” to verify the cartridge's commercial acceptability, the cartridge is released from a predetermined altitude onto a hard surface. A standard-life cartridge passes such a test because its internal components can resist the force of the toner load in the tank as it rapidly decelerates on impact. However, the increased mass and volume of the toner load in an extended life cartridge may cause some toner to be forced through the seal between the doctor blade and developer roller, and exit the cartridge. Other causes of toner loss can include (but are not limited to) vibration encountered during shipment and handling. In normal commerce, it is highly undesirable for a delivered cartridge to exhibit lost toner, as it leads to messy work areas and clothing, and generally reduces the user's confidence in the quality and value of the unit.
Therefore, it is desirable to provide a system for preventing the exit of toner from a tank/developer assembly of a two-piece toner cartridge in both standard-life and extended-live units. This system should be inexpensive and easy to implement on existing cartridge designs and should avoid the need to redesign any cartridge components. This system should also be straightforward to manipulate by a user and should ensure minimal or no loss of toner for both standard-life and extended-life toner cartridges of a variety of types and from a variety of manufacturers.